Source of Igniton

DOE-HDBK-1092-2004

outdoors or in corrosive atmospheres, its material and finish should be such that maintenance

costs and shutdowns are minimized. (See Figure 5-2.)

Figure 5-2. Arcs and sparks are sources of ignition that produce enough heat to cause

an explosion if the air and gas mixture is between the lower and upper flammable

limits of the liquid involved.

5.2.1

SOURCES OF IGNITION

When flammable gases or combustible dusts are mixed in the proper proportion with air, a

source of energy is all that is needed to touch off an explosion. One prime source of energy is

electricity. During normal operation, equipment such as switches, circuit breakers, motor

starters, pushbutton stations or plugs, and receptacles can produce arcs or sparks when

contacts are opened and closed, which can easily cause ignition. Other energy hazards are

devices that produce heat, such as lighting fixtures and motors. Surface temperatures of these

devices may exceed the safe limits of many flammable atmospheres. Finally, many parts of the

electrical system can become potential sources of ignition in the event of insulation failure.

Included in this category are wiring (particularly splices), transformers, impedance coils,

solenoids, and other low-temperature devices without make-or-break contacts.

Nonelectrical sources such as sparks from metal can also easily cause ignition: a hammer, file,

or other tool dropped on masonry or on a nonferrous surface could be a hazard unless it is

made of nonsparking material. For this reason, portable electrical equipment is usually made

from aluminum or other material that will not produce sparks if it is dropped.

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